1. Field of the Invention
This invention relates to so-called lamellar emulsions of which the emulsion droplets are surrounded by a liquid-crystalline lamellar phase of lipid molecules and water and are thus particularly stabilized and which are particularly suitable for restoring the disturbed degree of order of damaged skin.
2. Discussion of Related Art
It is known from the technical literature that lamellar emulsions are capable of favorably influencing the water metabolism of the skin and of storing large amounts of moisture in the skin. According to G. Dahms, Cosmetics and Toiletries, Vol. 101, November 1986, pages 113-115, lamellar emulsions can be produced by using an oil with an emulsifier of similar structure. EP-A-0 641 557 recommends the use of a lipophilic surfactant, a hydrophilic surfactant and a free fatty acid as emulsifier components. According to WO 94/17830, sorbitan and sucrose fatty acid esters are used as emulsifiers while, according to WO 95/28913 A1, urea is additionally used for the production of lamellar emulsions.
It has now been found that it is not so much the nature of the oil or emulsifier as the choice of a suitable co-emulsifier which is crucial to the production of oil-in-water emulsions containing anisotropic lamellar phases.
Accordingly, the present invention relates to an oil-in-water emulsion with lamellar liquid crystalline phases containing a cosmetic oil or fatty component, a hydrophilic emulsifier and a lipophilic co-emulsifier, characterized in that the lipophilic co-emulsifier used is a lipid corresponding to the general formula R1xe2x80x94Oxe2x80x94R2, where R1 is a primary linear alkyl, alkenyl or acyl group containing 20 to 30 carbon atoms and R2 is hydrogen, a group with the formula xe2x80x94(CnH2nO)xxe2x80x94H, where x=1 or 2 and n=2-4, or a polyhydroxyalkyl group containing 4 to 6 carbon atoms and 2 to 5 hydroxyl groups.
The oil-in-water emulsions according to the invention may contain either a cosmetic oil or fatty component or a water-in-oil emulsion as the inner phase. In the latter case, the lamellar emulsions according to the invention are water-in-oil-in-water emulsions.
The lipophilic co-emulsifier R1xe2x80x94Oxe2x80x94R2 is preferably a behenic or erucyl derivative, in which R1 is a linear terminally substituted alkyl, alkenyl or acyl group containing 22 carbon atoms, in a quantity of 10 to 90% by weight of the oil phase. In a particularly preferred embodiment, behenyl alcohol is present as the lipophilic co-emulsifier in a quantity of 20 to 80% by weight, based on the oil phase as a whole.
Other suitable co-emulsifiers are products of the addition of 1 or 2 moles of ethylene oxide or propylene oxide onto behenyl alcohol, erucyl alcohol, arachidyl alcohol or even onto behenic acid or erucic acid. Finally, other suitable co-emulsifiers are the monoesters of C20-30 fatty acids with polyols such as, for example, pentaerythritol, trimethylol propane, diglycerol, sorbitol, glucose or methyl glucose, Examples of such products are, for example, sorbitan monobehenate or pentaerythritol monoerucate.
Suitable hydrophilic emulsifiers for the production of the oil-in-water emulsions according to the invention are any surfactants suitable for the emulsification of cosmetic oil and fatty components. These are, above all, ionic emulsifiers or nonionic emulsifiers with an HLB value of 8 to 18. The HLB value is a value which can be calculated from the structure of the molecule in accordance with the equation HLB=0.2xc3x97(100 xe2x88x92L) where L is the percentage by weight of the lipophilic alkyl, alkenyl or acyl groups in the molecule.
Suitable ionic emulsifiers are anionic, cationic, zwitterionic and amphoteric surfactants, preferably those containing a primary linear C12-18 alkyl or alkenyl group. Suitable anionic emulsifiers are, for example, the salts of C12-18 fatty acids, of sulfuric acid monoesters or phosphoric acid monoesters of C12-18 fatty alcohols, of C12-18 acyl isethionic acids, of C12-18 alkane sulfonic acids or of C12-18 acylamino acids. Cationic emulsifiers are, for example, cetyl trimethyl ammonium chloride or dimethoxyethyl hydroxyethyl methyl ammonium chloride. Suitable zwitterionic surfactants are, for example, betaine surfactants, such as stearamidopropyl dimethyl carboxymethyl ammonium betaine, while suitable amphoteric surfactants are, for example, cetyl aminopropionic acid or cocoamphocarboxyglycinate. Amine oxide surfactants are also suitable hydrophilic emulsifiers.
Suitable nonionic surfactants with HLB values of 8 to 18 are, in particular, products of the addition of ethylene oxide onto fatty acids, fatty alcohols, fatty acid alkanolamides, fatty acid monoglycerides, sorbitan fatty acid esters, methyl glucoside fatty acid esters or other lipids containing carboxyl, hydroxyl or amino groups; the percentage content of ethoxy groups formed should be at least 40% by weight. Other suitable nonionic surfactants are alkyl polyglucosides, sugar esters and polyglycerol fatty acid esters.
Suitable oil and fatty components are any vegetable, animal, mineral and synthetic oils, fats and waxes suitable for use on the human body for physiological and aesthetic reasons. Examples include paraffins, fatty acid esters of monohydric or polyhydric alcohols, for example triglycerides, fatty acid/fatty alcohol esters, fatty acid/dicarboxylic acid/polyol polyesters, fatty alcohol/diol/dicarboxylic acid polyesters, di-n-alkyl ethers, polyolefins or silicone oils. Liquid oils or mixtures of oils and waxes which are liquid at 20xc2x0 C. are preferably used. Monoesters suitable as oil components are, for example, the methyl esters and isopropyl esters of fatty acids containing 12 to 22 carbon atoms such as, for example, methyl laurate, methyl stearate, methyl oleate, methyl erucate, isopropyl palmitate, isopropyl myristate, isopropyl palmitate, isopropyl stearate, isopropyl oleate. Other suitable monoesters are, for example, n-butyl stearate, n-hexyl laurate, n-decyl oleate, isooctyl stearate, isononyl palmitate, isononyl isononanoate, 2-ethylhexyl palmitate, 2-ethylhexyl laurate, 2-hexyidecyl stearate, 2-octyldodecyl palmitate, oleyl oleate, oleyl erucate, erucyl oleate and esters obtainable from technical aliphatic alcohols mixture. and technical aliphatic carboxylic acids, for example esters of saturated and unsaturated fatty alcohols containing 12 to 22 carbon atoms and saturated and unsaturated fatty acids containing 12 to 22 carbon atoms which are obtainable from animal and vegetable fats. Naturally occurring monoester or wax ester mixtures, as present for example in jojoba oil or in sperm oil, are also suitable.
Suitable dicarboxylic acid esters are, for example, di-n-butyl adipate, di-n-butyl sebacate, di-(2-ethylhexyl)-adipate, di-(2-hexyldecyl)-succinate and diisotridecyl azelate. Suitable diol esters (III) are, for example, ethylene glycol dioleate, ethylene glycol diisotridecanoate, propylene glycol di-(2-ethylhexanoate), butanediol diisostearate and neopentyl glycol dicaprylate.
Suitable fatty acid triglycerides are natural vegetable oils, for example olive oil, sunflower oil, soybean oil, peanut oil, rapeseed oil, almond oil, palm oil and even the liquid fractions of coconut oil or palm oil, and animal oils such as, for example, neat""s foot oil, the liquid fractions of beef tallow or even synthetic triglycerides of the type obtained by esterifying glycerol with C8-22 fatty acids, for example triglycerides of caprylic acid/capric acid mixtures, triglycerides of technical oleic acid or palmitic acid mixtures.
The oil-in-water emulsions of cosmetic oil or fatty components containing lamellar liquid crystalline phases according to the invention are produced by methods known per se using hydrophilic emulsifiers and lipophilic co-emulsifiers, the aqueous phase which may contain hydrophilic emulsifiers being intensively mixed with the oil or fatty phase which contains as lipophilic co-emulsifiers at least one lipid corresponding to the general formula R1xe2x80x94Oxe2x80x94R2, where R1 is a linear alkyl, alkenyl or acyl group containing 20 to 30 carbon atoms and R2 is hydrogen, a group with the formula xe2x80x94CnH2nO)xxe2x80x94H, where x=1 or 2 and n=2-4, or a polyhydroxyalkyl group containing 4 to 6 carbon atoms and 2 to 5 hydroxyl groups.
The aqueous phase contains all the water-soluble components, for example a water-soluble emulsifier, the preservatives, buffer salts, magnesium chloride, propylene glycol, glycerol, water-soluble polymeric thickeners or water-soluble cosmetic active substances.
Besides the cosmetic oils and fats, the oil-soluble emulsifiers and, in particular, the lipophilic co-emulsifier are added to the oil phase. Finally, other oil-soluble auxiliaries optionally present, for example oil-soluble antioxidants or preservatives, waxes, silicones and the oil-soluble cosmetic active substances, are also added to the oil phase. The oil phase is then heated to a temperature at which it is present as a clear homogeneous melt. The aqueous phase is also heated to the same temperature. The oil phase and the water phase are then intensively mixed with one another.
Where a nonionic emulsifier with a phase inversion temperature below 100xc2x0 C. is used, the emulsion is preferably prepared at that temperature or is heated to that temperature during emulsification. The emulsion thus becomes a water-in-oil emulsion which then inverts back into an o/w emulsion when the temperature falls below the phase inversion temperature and which accumulates in a particularly fine-droplet, low-viscosity and storage-stable form.
The addition of perfumes and particularly readily volatile or heat-sensitive substances is preferably carried out after cooling to temperatures of 40xc2x0 C. or lower.
The lamellar emulsions according to the invention may be thinly liquid or cream-like according to the type and quantity of the inner phase. Their consistency can also be controlled to a certain extent by thickeners or by the emulsification process, i.e. through the droplet fineness.
The oil-in-water emulsions according to the invention retain their lamellarity irrespective of the ratio by weight of oil phase to water phase. In other words, the oil droplets retain their liquid crystalline lipid double layer shell even after heavy dilution with water. By virtue of their birefringent properties, they can be made visible in polarized light.
The lamellar emulsions according to the invention are suitable for skin care. Not only do they increase the moisture retention capacity of the skin, they also increase the degree of order of the epidermis and improve the barrier function of the skin. After skin damage, for example by surfactants or mechanical stressing, treatment with the lamellar cream according to the invention leads more quickly to restoration of the lamellarity of the epidermal lipid structures.
Accordingly, the present invention also relates to the use of an oil-in-water emulsion with lamellar liquid crystalline phases containing a cosmetic oil or fatty component, a hydrophilic emulsifier and a lipophilic co-emulsifier which is a lipid corresponding to the general formula R1xe2x80x94Oxe2x80x94R2, where R1 is a primary linear alkyl, alkenyl or acyl group containing 20 to 30 carbon atoms and R2 is hydrogen, a group with the formula xe2x80x94(CnH2nO)xxe2x80x94H, where xxe2x88x921 or 2 and n=2-4, or a polyhydroxyalkyl group containing 4 to 6 carbon atoms and 2 to 5 hydroxyl groups, for restoring the lamellarity and degree of order of the epidermal lipid structures of damaged skin.
This effect of the lamellar oil-in-water emulsions according to the invention can be experimentally demonstrated by infrared-spectroscopic examination of the conformation order of the xe2x80x94(CH2)xxe2x80x94chains of the lipids of the stratum corneum. The position of the stretching vibrational bands vs(CH2) and vas (CH2) (ca. 2850 cmxe2x88x921 and 2915 cmxe2x88x921) is dependent on the percentage of higher-energy xe2x80x9cgauchexe2x80x9d conformers of a lipid chain as opposed to the lower-energy (all-trans) conformers. Increasing disorder of the lipid membrane leads to a displacement of these bands to higher frequencies (up to a few cmxe2x88x921) on account of the increase in the percentage of the higher-energy vibrations of the xe2x80x9cgauchexe2x80x9d conformers (cf. R. O. Potts, M. L. Francoeur: Infrared Spectroscopy of Stratum Corneum Lipids in: Pharmaceutical Skin Penetration Enhancement, ed. by Kenneth A. Walters, Jonathan Hadgraft, 1993, pages 269-291).
Using a piece of skin damaged by washing with lauryl sulfate solution, it can be shown that an increase in the conformation order (xe2x80x9clamellarityxe2x80x9d) of the epidermal lipids can be achieved in a few days by treatment with a lamellar cream according to the invention.